Phthalocyanines have great promise as sensitizers for photodynamic therapy (PDT) of cancer. We have shown that certain tertiary and quaternary amines linked to the metal can improve the cellular uptake and photosensitizing properties of these compounds. The proposed research will test the hypothesis that amine moieties linked to appropriate metals within the phthalocyanine ring can provide highly efficient photosensitization. Aim I: The phthalocyanines synthesized in Project 1 will be screened for photosensitizing efficiency in vitro. Measurements will include cellular uptake and intracellular distribution of the new phthalocyanines, as well as clonogenic cell survival. Aim II: Cellular targets of photodynamic action will be identified. Drugs varying in photosensitizing activity will be compared with respect to damage induced in the plasma membrane, mitochondria, and nuclei, and their mutagenic potential will be ascertained. Aim III: TO investigate processes involved in PDT cytotoxicity, (a) direct tumor cell killing and (b) the altered environment of tumors following PDT will be studied by exposing PDT-treated cells to growth-limiting conditions which approximate in vivo conditions. The involvement of DNA degradation in post-treatment interactions of PDT with ionizing radiation-induced damage will be explored as will the potential of two-photon photochemical processes. Aim IV: Attempts will be made to augment PDT-induced damage by other membrane-active agents. Mechanisms of the marked enhancement of photodynamic cell killing by the ionophore nigericin and possibly other membrane-active agents will good potential as photosensitizers for PDT, elucidate important aspects of the mechanisms of photosensitization of cells and tumors, and contribute to an understanding of the structure-activity relationships for this class of compounds.